In vitro translation of Rous sarcoma virus RNA and identification of two protein products believed to be derived from the sarc gene: During the last year we have compared the 35S-labeled translation products of RNA from wild type nondefective (nd) transforming Rous sarcoma virus, Prague B strain with RNA from a corresponding transformation-defective (td) Prague B derivative. Translation was accomplished by use of a rabbit reticulocyte lysate system that had been treated with a calcium-dependent micrococcal nuclease to digest endogenous RNA. Upon addition of a calcium chelator, EGTA, translation of the viral RNAs was accomplished in the presence of 35S-methionine. The protein products were subjected to electrophoresis on polyacrylamide gel slabs, which were then placed on film for autoradiography. The patterns of the labeled proteins produced with the two viral RNAs were identical except for two protein bands at 25,000 and 18,000 daltons which were present in the translation products from RNA of the nd but not the td Rous sarcoma virus. We presently believe that these proteins were produced by translation of the sarc or transforming gene of the nd virus. We are currently examining the protein products of RNA from temperature-sensitive mutants in the transformation genome in hope of finding physical variations of the mutated proteins (in the 25,000 and 18,000 range) that would provide further proof of their identity with a transformation protein. We are also preparing, in purified form, sufficient protein for injection into rabbits for synthesis of antibodies. We would then attempt to locate the transformation proteins in their undenatured form in lysates of RSV-infected chick embryo fibroblasts.